Most refining processes limit the concentration of salt compounds (most of which contain alkaline compounds) of the incoming crude oil feed. These salt compounds can be corrosive to the equipment used for processing and can also be poisonous to catalysts that are widely used in modern refining processes. Whole crudes vary in their salt content depending on their origin. While desalters can remove alkaline compounds from crude oil, desalters typically require a significant amount of energy and possibly additional injected chemicals. Additionally, the level of alkaline compounds remaining in the treated crude oil can still cause plugging problems in processes using supercritical water.
Supercritical water has characteristics that can be used to upgrade crude oil. For instance, the sharp decrease of the dielectric constant of water at and around its critical point makes alkaline compounds insoluble in supercritical water. The low solubility of alkaline compounds in supercritical water induces precipitation of alkaline compounds during processing of crude oil. During traditional processing of crude oil, the precipitate can then cause plugging and corrosion of reactors or downstream units such as heat exchangers. This can result in unexpected shut-down of the crude oil processing unit.
The present invention advantageously provides a process and apparatus for upgrading crude oil through the use of supercritical water while avoiding the clogging of the equipment by alkaline compounds that are present in various amounts in crude oil.